This invention relates, in general, to redundant signal circuits; and in particular, this invention relates to control systems for rotating machines.
Turbomachines are dependable operators which may perform for many years without an unscheduled shutdown. However, the reliability of a turbomachine is dependent upon many different parts and, in particular, the control system of the machine. Machines which utilize the so called mechanical hydraulic controls achieve great reliability through careful manufacture and maintenance. Machines which utilize electronic controls may operate with increased reliability through redundant controls packages not possible with the larger mechanical hydraulic controls.
U.S. Pat. No. 4,025,762 issued May 24, 1977 and assigned to the assignee of the present invention shows one example of a turbomachine controls system and is incorporated into this application by this reference thereto. Speed control of the turbomachine is achieved by positioning a steam valve which controls the amount of inlet steam to the turbine. The steam valve is controlled by a valve operator which, in turn, is electronically controlled by a speed error signal. The speed error signal is derived from the electronic summation of a speed reference signal and a speed feedback signal. The speed feedback signal is obtained through an electronic device well known in the art and which may include a shaft mounted toothed wheel having a magnetic pick-up in proximity thereto. It is clear, that in order for the automatic turbine control system to operate, the feedback speed signal must be operative. To ensure continued availability of a speed feedback signal, the present invention provides for redundant speed pick-ups and dual signal channels with switching logic there between so that if one signal channel becomes inoperative, the other signal channel will supply a valid speed feedback signal.
The foregoing continued availability of a speed feedback signal is implemented through the use of electronic circuitry which includes dual J-K flip-flops with clear. This device receives at least a portion of each of two redundant speed feedback signals. One signal is used to clear the other signal in the device. Should the clear signal fail, then the other signal takes over as the dominant signal.
It is one object of the present invention to provide a redundant signal circuit which will tolerate failure to either one of two signal inputs and still remain operative.
It is a corollary object of the present invention to provide a signal circuit which will remain operative even as one or the other signal inputs is being replaced.
While the present invention is set forth in terms of a speed feedback device, it is not intended that it be so limited. The present invention is applicable to any redundant signal device wherein it is desirable to maintain an output signal despite failure of one of the two input signals. The noval features believed characteristic of the present invention are set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof, may best be understood with reference to the following description, taken in connection with the drawings.